Relative Humidity Formula Dry Bulb Wet Bulb

Relative humidity is measured using a device called a sling psychrometer this consists of 2 side by side conventional thermometers one of which the wet bulb thermometer has a wetted wick placed at the bottom the other the dry bulb thermometer has no wetted wick.

Relative humidity formula dry bulb wet bulb. The dry bulb wet bulb and dew point temperatures are important to determine the state of humid air. It includes a dry bulb thermometer a wet bulb thermometer and a psychrometric chart a graph that plots the relationships between the dry and wet bulb temperature relative humidity and dew point at constant pressure. At 100 relative humidity the wet bulb temperature is equal to the air temperature dry bulb temperature. The dry bulb temperature is the ambient temperature.

Given the wet bulb temperature dry bulb temperature and ambient pressure the humidity of the air can be calculated as follows. By definition wet bulb temperature is the lowest temperature a portion of air can acquire by evaporative cooling only. Enter your actual station pressure not the altimeter setting. The difference between these two temperatures is a measure of the humidity of the air.

If the dry and wet bulb temperatures are set to the same value the calculator will show the saturation mixing ratio the amount of water in saturated air at that temperature. Enter your actual station pressure not the altimeter setting. When the psychrometer is swung around by its attached chain or handle the air causes the water on the wick to evaporate which. In of mercury mm of mercury millibars hpa.

At lower humidity the wet bulb temperature is lower than dry bulb temperature because of evaporative cooling. In of mercury mm of mercury millibars hpa. Enter a temperature relative humidity and actual station pressure. The higher the difference in these temperatures the lower is the humidity.

The knowledge of only two of these values is enough to determine the state of the moist air including the content of water vapor and the sensible and latent energy enthalpy in the air. If the air is fully saturated 100 relative humidity the water cannot evaporate so both the wet and dry bulb temperatures are the same. The state of air with dry bulb temperature 75 o f and wet bulb temperature 62 5 o f can be visualized in the psychrometric chart as indicated below.